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Carbon dating is an extremely important method for determining the age of ancient organic matter. The method relies on measurements of radioactive carbon-14 produced by cosmic rays and incorporated into the bodies of animals and plants. As Bard discusses in his Perspective, the accuracy of the technique depends on quantifying the production rates of cosmogenic isotopes over time. Results presented in the same issue by Plummer et al. shed light on the past history of the important chlorine-36 isotope, which in turn offers clues on how the geomagnetic field has influenced cosmic ray production of other isotopes.
Édouard Bard (Fri,) studied this question.